gdb/elfread.c

   1 /* Read ELF (Executable and Linking Format) object files for GDB.
   2    Copyright 1991, 1992 Free Software Foundation, Inc.
   3    Written by Fred Fish at Cygnus Support.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 /************************************************************************
  22  *                                                                      *
  23  *                              NOTICE                                  *
  24  *                                                                      *
  25  * This file is still under construction.  When it is complete, this    *
  26  * notice will be removed.  Until then, direct any questions or changes *
  27  * to Fred Fish at Cygnus Support (fnf@cygnus.com)                      *
  28  *                                                                      *
  29  * FIXME        Still needs support for shared libraries.               *
  30  * FIXME        Still needs support for core files.                     *
  31  * FIXME        The ".debug" and ".line" section names are hardwired.   *
  32  *                                                                      *
  33  ************************************************************************/
  34
  35 #include "defs.h"
  36 #include "elf/common.h"
  37 #include "elf/external.h"
  38 #include "elf/internal.h"
  39 #include "bfd.h"
  40 #include "libbfd.h"             /* For bfd_elf_find_section */
  41 #include "symtab.h"
  42 #include "symfile.h"
  43 #include "objfiles.h"
  44 #include "buildsym.h"
  45 #include "gdb-stabs.h"
  46 #include "complaints.h"
  47 #include <string.h>
  48
  49 #define STREQ(a,b) (strcmp((a),(b))==0)
  50
  51 /* The struct elfinfo is available only during ELF symbol table and
  52    psymtab reading.  It is destroyed at the complation of psymtab-reading.
  53    It's local to elf_symfile_read.  */
  54
  55 struct elfinfo {
  56   file_ptr dboffset;            /* Offset to dwarf debug section */
  57   unsigned int dbsize;          /* Size of dwarf debug section */
  58   file_ptr lnoffset;            /* Offset to dwarf line number section */
  59   unsigned int lnsize;          /* Size of dwarf line number section */
  60   asection *stabsect;           /* Section pointer for .stab section */
  61   asection *stabindexsect;      /* Section pointer for .stab.index section */
  62 };
  63
  64 /* Various things we might complain about... */
  65
  66 struct complaint section_info_complaint =
  67   {"elf/stab section information %s without a preceding file symbol", 0, 0};
  68
  69 struct complaint section_info_dup_complaint =
  70   {"duplicated elf/stab section information for %s", 0, 0};
  71
  72 struct complaint stab_info_mismatch_complaint =
  73   {"elf/stab section information missing for %s", 0, 0};
  74
  75 struct complaint stab_info_questionable_complaint =
  76   {"elf/stab section information questionable for %s", 0, 0};
  77
  78 static void
  79 elf_symfile_init PARAMS ((struct objfile *));
  80
  81 static void
  82 elf_new_init PARAMS ((struct objfile *));
  83
  84 static void
  85 elf_symfile_read PARAMS ((struct objfile *, struct section_offsets *, int));
  86
  87 static void
  88 elf_symfile_finish PARAMS ((struct objfile *));
  89
  90 static void
  91 elf_symtab_read PARAMS ((bfd *,  CORE_ADDR, struct objfile *));
  92
  93 static void
  94 free_elfinfo PARAMS ((PTR));
  95
  96 static struct section_offsets *
  97 elf_symfile_offsets PARAMS ((struct objfile *, CORE_ADDR));
  98
  99 #if 0
 100 static void
 101 record_minimal_symbol PARAMS ((char *, CORE_ADDR, enum minimal_symbol_type,
 102                                struct objfile *));
 103 #endif
 104
 105 static void
 106 record_minimal_symbol_and_info PARAMS ((char *, CORE_ADDR,
 107                                         enum minimal_symbol_type, char *,
 108                                         struct objfile *));
 109
 110 static void
 111 elf_locate_sections PARAMS ((bfd *, asection *, PTR));
 112
 113 /* We are called once per section from elf_symfile_read.  We
 114    need to examine each section we are passed, check to see
 115    if it is something we are interested in processing, and
 116    if so, stash away some access information for the section.
 117
 118    For now we recognize the dwarf debug information sections and
 119    line number sections from matching their section names.  The
 120    ELF definition is no real help here since it has no direct
 121    knowledge of DWARF (by design, so any debugging format can be
 122    used).
 123
 124    We also recognize the ".stab" sections used by the Sun compilers
 125    released with Solaris 2.
 126
 127    FIXME:  The section names should not be hardwired strings. */
 128
 129 static void
 130 elf_locate_sections (ignore_abfd, sectp, eip)
 131      bfd *ignore_abfd;
 132      asection *sectp;
 133      PTR eip;
 134 {
 135   register struct elfinfo *ei;
 136
 137   ei = (struct elfinfo *) eip;
 138   if (STREQ (sectp -> name, ".debug"))
 139     {
 140       ei -> dboffset = sectp -> filepos;
 141       ei -> dbsize = bfd_get_section_size_before_reloc (sectp);
 142     }
 143   else if (STREQ (sectp -> name, ".line"))
 144     {
 145       ei -> lnoffset = sectp -> filepos;
 146       ei -> lnsize = bfd_get_section_size_before_reloc (sectp);
 147     }
 148   else if (STREQ (sectp -> name, ".stab"))
 149     {
 150       ei -> stabsect = sectp;
 151     }
 152   else if (STREQ (sectp -> name, ".stab.index"))
 153     {
 154       ei -> stabindexsect = sectp;
 155     }
 156 }
 157
 158 #if 0   /* Currently unused */
 159
 160 char *
 161 elf_interpreter (abfd)
 162      bfd *abfd;
 163 {
 164   sec_ptr interp_sec;
 165   unsigned size;
 166   char *interp = NULL;
 167
 168   interp_sec = bfd_get_section_by_name (abfd, ".interp");
 169   if (interp_sec)
 170     {
 171       size = bfd_section_size (abfd, interp_sec);
 172       interp = alloca (size);
 173       if (bfd_get_section_contents (abfd, interp_sec, interp, (file_ptr)0,
 174                                     size))
 175         {
 176           interp = savestring (interp, size - 1);
 177         }
 178       else
 179         {
 180           interp = NULL;
 181         }
 182     }
 183   return (interp);
 184 }
 185
 186 #endif
 187
 188 /*
 189
 190 LOCAL FUNCTION
 191
 192         record_minimal_symbol -- add entry to minimal symbol table
 193
 194 SYNOPSIS
 195
 196         static void record_minimal_symbol (char *name, CORE_ADDR address)
 197
 198 DESCRIPTION
 199
 200         Given a pointer to the name of a symbol that should be added to the
 201         minimal symbol table and the address associated with that symbol, records
 202         this information for later use in building the minimal symbol table.
 203
 204  */
 205
 206 #if 0   /* FIXME:  Unused */
 207
 208 static void
 209 record_minimal_symbol (name, address, ms_type, objfile)
 210      char *name;
 211      CORE_ADDR address;
 212      enum minimal_symbol_type ms_type;
 213      struct objfile *objfile;
 214 {
 215   name = obsavestring (name, strlen (name), &objfile -> symbol_obstack);
 216   prim_record_minimal_symbol (name, address, ms_type);
 217 }
 218
 219 #endif
 220
 221 static void
 222 record_minimal_symbol_and_info (name, address, ms_type, info, objfile)
 223      char *name;
 224      CORE_ADDR address;
 225      enum minimal_symbol_type ms_type;
 226      char *info;                /* FIXME, is this really char *? */
 227      struct objfile *objfile;
 228 {
 229   name = obsavestring (name, strlen (name), &objfile -> symbol_obstack);
 230   prim_record_minimal_symbol_and_info (name, address, ms_type, info);
 231 }
 232
 233 /*
 234
 235 LOCAL FUNCTION
 236
 237         elf_symtab_read -- read the symbol table of an ELF file
 238
 239 SYNOPSIS
 240
 241         void elf_symtab_read (bfd *abfd, CORE_ADDR addr,
 242                               struct objfile *objfile)
 243
 244 DESCRIPTION
 245
 246         Given an open bfd, a base address to relocate symbols to, and a
 247         flag that specifies whether or not this bfd is for an executable
 248         or not (may be shared library for example), add all the global
 249         function and data symbols to the minimal symbol table.
 250
 251         In stabs-in-ELF, as implemented by Sun, there are some local symbols
 252         defined in the ELF symbol table, which can be used to locate
 253         the beginnings of sections from each ".o" file that was linked to
 254         form the executable objfile.  We gather any such info and record it
 255         in data structures hung off the objfile's private data.
 256
 257 */
 258
 259 static void
 260 elf_symtab_read (abfd, addr, objfile)
 261      bfd *abfd;
 262      CORE_ADDR addr;
 263      struct objfile *objfile;
 264 {
 265   unsigned int storage_needed;
 266   asymbol *sym;
 267   asymbol **symbol_table;
 268   unsigned int number_of_symbols;
 269   unsigned int i;
 270   int index;
 271   struct cleanup *back_to;
 272   CORE_ADDR symaddr;
 273   enum minimal_symbol_type ms_type;
 274   /* If sectinfo is nonzero, it contains section info that should end up
 275      filed in the objfile.  */
 276   struct stab_section_info *sectinfo = 0;
 277   /* If filesym is nonzero, it points to a file symbol, but we haven't
 278      seen any section info for it yet.  */
 279   asymbol *filesym = 0;
 280   struct dbx_symfile_info *dbx = (struct dbx_symfile_info *)
 281                                  objfile->sym_private;
 282
 283   storage_needed = get_symtab_upper_bound (abfd);
 284
 285   if (storage_needed > 0)
 286     {
 287       symbol_table = (asymbol **) xmalloc (storage_needed);
 288       back_to = make_cleanup (free, symbol_table);
 289       number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
 290
 291       for (i = 0; i < number_of_symbols; i++)
 292         {
 293           sym = symbol_table[i];
 294           /* Select global/weak symbols that are defined in a specific section.
 295              Note that bfd now puts abs symbols in their own section, so
 296              all symbols we are interested in will have a section. */
 297           if ((sym -> flags & (BSF_GLOBAL | BSF_WEAK))
 298               && (sym -> section != NULL))
 299             {
 300               symaddr = sym -> value;
 301               /* Relocate all non-absolute symbols by base address.  */
 302               if (sym -> section != &bfd_abs_section)
 303                 symaddr += addr;
 304
 305               /* For non-absolute symbols, use the type of the section
 306                  they are relative to, to intuit text/data.  Bfd provides
 307                  no way of figuring this out for absolute symbols. */
 308               if (sym -> section -> flags & SEC_CODE)
 309                 {
 310                   ms_type = mst_text;
 311                 }
 312               else if (sym -> section -> flags & SEC_DATA)
 313                 {
 314                   ms_type = mst_data;
 315                 }
 316               else
 317                 {
 318                   /* FIXME:  Solaris2 shared libraries include lots of
 319                      odd "absolute" and "undefined" symbols, that play
 320                      hob with actions like finding what function the PC
 321                      is in.  Ignore them if they aren't text or data.  */
 322                   /* ms_type = mst_unknown; */
 323                   continue;             /* Skip this symbol. */
 324                 }
 325               /* Pass symbol size field in via BFD.  FIXME!!!  */
 326               record_minimal_symbol_and_info ((char *) sym -> name,
 327                          symaddr, ms_type, sym->udata, objfile);
 328             }
 329
 330           /* See if this is a debugging symbol that helps Solaris
 331              stabs-in-elf debugging.  */
 332
 333           else if (sym->flags & BSF_FILE)
 334             {
 335               /* Chain any old one onto the objfile; remember new sym.  */
 336               if (sectinfo)
 337                 {
 338                     sectinfo->next = dbx->stab_section_info;
 339                     dbx->stab_section_info = sectinfo;
 340                     sectinfo = 0;
 341                 }
 342               filesym = sym;
 343             }
 344           else if ((sym->flags & BSF_LOCAL) &&
 345                    (sym->section) &&
 346                    (sym->section->flags & SEC_DATA) &&
 347                    (sym->name))
 348             {
 349               /* Named Local variable in a Data section.  Check its name.  */
 350               index = -1;
 351               switch (sym->name[1])
 352                 {
 353                   case 'b':
 354                         if (!strcmp ("Bbss.bss", sym->name))
 355                           index = SECT_OFF_BSS;
 356                         break;
 357                   case 'd':
 358                         if (!strcmp ("Ddata.data", sym->name))
 359                           index = SECT_OFF_DATA;
 360                         break;
 361                   case 'r':
 362                         if (!strcmp ("Drodata.rodata", sym->name))
 363                           index = SECT_OFF_RODATA;
 364                         break;
 365                 }
 366               if (index > 0)
 367                 {
 368                   /* We have some new info.  Allocate a sectinfo, if
 369                      needed, and fill it in.  */
 370                   if (!sectinfo)
 371                     {
 372                       sectinfo = (struct stab_section_info *)
 373                                  xmmalloc (objfile -> md,
 374                                            sizeof (*sectinfo));
 375                       memset ((PTR) sectinfo, 0, sizeof (*sectinfo));
 376                       if (!filesym)
 377                         complain (&section_info_complaint, sym->name);
 378                       else
 379                         sectinfo->filename = (char *)filesym->name;
 380                     }
 381                   if (sectinfo->sections[index])
 382                     complain (&section_info_dup_complaint, sectinfo->filename);
 383
 384                   symaddr = sym -> value;
 385                   /* Relocate all non-absolute symbols by base address.  */
 386                   if (sym -> section != &bfd_abs_section)
 387                       symaddr += addr;
 388                   sectinfo->sections[index] = symaddr;
 389                 }
 390             }
 391         }
 392       do_cleanups (back_to);
 393     }
 394 }
 395
 396 /* Scan and build partial symbols for a symbol file.
 397    We have been initialized by a call to elf_symfile_init, which
 398    currently does nothing.
 399
 400    SECTION_OFFSETS is a set of offsets to apply to relocate the symbols
 401    in each section.  We simplify it down to a single offset for all
 402    symbols.  FIXME.
 403
 404    MAINLINE is true if we are reading the main symbol
 405    table (as opposed to a shared lib or dynamically loaded file).
 406
 407    This function only does the minimum work necessary for letting the
 408    user "name" things symbolically; it does not read the entire symtab.
 409    Instead, it reads the external and static symbols and puts them in partial
 410    symbol tables.  When more extensive information is requested of a
 411    file, the corresponding partial symbol table is mutated into a full
 412    fledged symbol table by going back and reading the symbols
 413    for real.
 414
 415    We look for sections with specific names, to tell us what debug
 416    format to look for:  FIXME!!!
 417
 418    dwarf_build_psymtabs() builds psymtabs for DWARF symbols;
 419    elfstab_build_psymtabs() handles STABS symbols.
 420
 421    Note that ELF files have a "minimal" symbol table, which looks a lot
 422    like a COFF symbol table, but has only the minimal information necessary
 423    for linking.  We process this also, and use the information to
 424    build gdb's minimal symbol table.  This gives us some minimal debugging
 425    capability even for files compiled without -g.  */
 426
 427 static void
 428 elf_symfile_read (objfile, section_offsets, mainline)
 429      struct objfile *objfile;
 430      struct section_offsets *section_offsets;
 431      int mainline;
 432 {
 433   bfd *abfd = objfile->obfd;
 434   struct elfinfo ei;
 435   struct cleanup *back_to;
 436   CORE_ADDR offset;
 437
 438   init_minimal_symbol_collection ();
 439   back_to = make_cleanup (discard_minimal_symbols, 0);
 440
 441   memset ((char *) &ei, 0, sizeof (ei));
 442
 443   /* Allocate struct to keep track of the symfile */
 444   objfile->sym_private = (PTR)
 445     xmmalloc (objfile -> md, sizeof (struct dbx_symfile_info));
 446   memset ((char *) objfile->sym_private, 0, sizeof (struct dbx_symfile_info));
 447   make_cleanup (free_elfinfo, (PTR) objfile);
 448
 449   /* Process the normal ELF symbol table first.  This may write some
 450      chain of info into the dbx_symfile_info in objfile->sym_private,
 451      which can later be used by elfstab_offset_sections.  */
 452
 453   /* FIXME, should take a section_offsets param, not just an offset.  */
 454   offset = ANOFFSET (section_offsets, 0);
 455   elf_symtab_read (abfd, offset, objfile);
 456
 457   /* Now process debugging information, which is contained in
 458      special ELF sections.  We first have to find them... */
 459
 460   bfd_map_over_sections (abfd, elf_locate_sections, (PTR) &ei);
 461   if (ei.dboffset && ei.lnoffset)
 462     {
 463       /* DWARF sections */
 464       dwarf_build_psymtabs (objfile,
 465                             section_offsets, mainline,
 466                             ei.dboffset, ei.dbsize,
 467                             ei.lnoffset, ei.lnsize);
 468     }
 469   if (ei.stabsect)
 470     {
 471       /* STABS sections */
 472
 473       /* FIXME:  Sun didn't really know how to implement this well.
 474          They made .stab sections that don't point to the .stabstr
 475          section with the sh_link field.  BFD doesn't make string table
 476          sections visible to the caller.  So we have to search the
 477          ELF section table, not the BFD section table, for the string
 478          table.  */
 479       struct elf_internal_shdr *elf_sect;
 480
 481       elf_sect = bfd_elf_find_section (abfd, ".stabstr");
 482       if (elf_sect)
 483         elfstab_build_psymtabs (objfile,
 484           section_offsets,
 485           mainline,
 486           ei.stabsect->filepos,                         /* .stab offset */
 487           bfd_get_section_size_before_reloc (ei.stabsect),/* .stab size */
 488           (file_ptr) elf_sect->sh_offset,               /* .stabstr offset */
 489           elf_sect->sh_size);                           /* .stabstr size */
 490     }
 491
 492   if (!have_partial_symbols ())
 493     {
 494       wrap_here ("");
 495       printf_filtered ("(no debugging symbols found)...");
 496       wrap_here ("");
 497     }
 498
 499   /* Install any minimal symbols that have been collected as the current
 500      minimal symbols for this objfile. */
 501
 502   install_minimal_symbols (objfile);
 503
 504   do_cleanups (back_to);
 505 }
 506
 507 /* This cleans up the objfile's sym_private pointer, and the chain of
 508    stab_section_info's, that might be dangling from it.  */
 509
 510 static void
 511 free_elfinfo (objp)
 512      PTR objp;
 513 {
 514   struct objfile *objfile = (struct objfile *)objp;
 515   struct dbx_symfile_info *dbxinfo = (struct dbx_symfile_info *)
 516                                      objfile->sym_private;
 517   struct stab_section_info *ssi, *nssi;
 518
 519   ssi = dbxinfo->stab_section_info;
 520   while (ssi)
 521     {
 522       nssi = ssi->next;
 523       mfree (objfile->md, ssi);
 524       ssi = nssi;
 525     }
 526
 527   dbxinfo->stab_section_info = 0;       /* Just say No mo info about this.  */
 528 }
 529
 530
 531 /* Initialize anything that needs initializing when a completely new symbol
 532    file is specified (not just adding some symbols from another file, e.g. a
 533    shared library).
 534
 535    We reinitialize buildsym, since we may be reading stabs from an ELF file.  */
 536
 537 static void
 538 elf_new_init (ignore)
 539      struct objfile *ignore;
 540 {
 541   stabsread_new_init ();
 542   buildsym_new_init ();
 543 }
 544
 545 /* Perform any local cleanups required when we are done with a particular
 546    objfile.  I.E, we are in the process of discarding all symbol information
 547    for an objfile, freeing up all memory held for it, and unlinking the
 548    objfile struct from the global list of known objfiles. */
 549
 550 static void
 551 elf_symfile_finish (objfile)
 552      struct objfile *objfile;
 553 {
 554   if (objfile -> sym_private != NULL)
 555     {
 556       mfree (objfile -> md, objfile -> sym_private);
 557     }
 558 }
 559
 560 /* ELF specific initialization routine for reading symbols.
 561
 562    It is passed a pointer to a struct sym_fns which contains, among other
 563    things, the BFD for the file whose symbols are being read, and a slot for
 564    a pointer to "private data" which we can fill with goodies.
 565
 566    For now at least, we have nothing in particular to do, so this function is
 567    just a stub. */
 568
 569 static void
 570 elf_symfile_init (ignore)
 571      struct objfile *ignore;
 572 {
 573 }
 574
 575 /* ELF specific parsing routine for section offsets.
 576
 577    Plain and simple for now.  */
 578
 579 static
 580 struct section_offsets *
 581 elf_symfile_offsets (objfile, addr)
 582      struct objfile *objfile;
 583      CORE_ADDR addr;
 584 {
 585   struct section_offsets *section_offsets;
 586   int i;
 587
 588   section_offsets = (struct section_offsets *)
 589     obstack_alloc (&objfile -> psymbol_obstack,
 590                    sizeof (struct section_offsets) +
 591                           sizeof (section_offsets->offsets) * (SECT_OFF_MAX-1));
 592
 593   for (i = 0; i < SECT_OFF_MAX; i++)
 594     ANOFFSET (section_offsets, i) = addr;
 595
 596   return section_offsets;
 597 }
 598 \f
 599 /* When handling an ELF file that contains Sun STABS debug info,
 600    some of the debug info is relative to the particular chunk of the
 601    section that was generated in its individual .o file.  E.g.
 602    offsets to static variables are relative to the start of the data
 603    segment *for that module before linking*.  This information is
 604    painfully squirreled away in the ELF symbol table as local symbols
 605    with wierd names.  Go get 'em when needed.  */
 606
 607 void
 608 elfstab_offset_sections (objfile, pst)
 609      struct objfile *objfile;
 610      struct partial_symtab *pst;
 611 {
 612   char *filename = pst->filename;
 613   struct dbx_symfile_info *dbx = (struct dbx_symfile_info *)
 614                                  objfile->sym_private;
 615   struct stab_section_info *maybe = dbx->stab_section_info;
 616   struct stab_section_info *questionable = 0;
 617   int i;
 618   char *p;
 619
 620   /* The ELF symbol info doesn't include path names, so strip the path
 621      (if any) from the psymtab filename.  */
 622   while (0 != (p = strchr (filename, '/')))
 623     filename = p+1;
 624
 625   /* FIXME:  This linear search could speed up significantly
 626      if it was chained in the right order to match how we search it,
 627      and if we unchained when we found a match. */
 628   for (; maybe; maybe = maybe->next)
 629     {
 630       if (filename[0] == maybe->filename[0]
 631           && !strcmp (filename, maybe->filename))
 632         {
 633           /* We found a match.  But there might be several source files
 634              (from different directories) with the same name.  */
 635           if (0 == maybe->found)
 636             break;
 637           questionable = maybe;         /* Might use it later.  */
 638         }
 639     }
 640
 641   if (maybe == 0 && questionable != 0)
 642     {
 643       complain (&stab_info_questionable_complaint, filename);
 644       maybe = questionable;
 645     }
 646
 647   if (maybe)
 648     {
 649       /* Found it!  Allocate a new psymtab struct, and fill it in.  */
 650       maybe->found++;
 651       pst->section_offsets = (struct section_offsets *)
 652         obstack_alloc (&objfile -> psymbol_obstack,
 653                        sizeof (struct section_offsets) +
 654                sizeof (pst->section_offsets->offsets) * (SECT_OFF_MAX-1));
 655
 656       for (i = 0; i < SECT_OFF_MAX; i++)
 657         ANOFFSET (pst->section_offsets, i) = maybe->sections[i];
 658       return;
 659     }
 660
 661   /* We were unable to find any offsets for this file.  Complain.  */
 662   if (dbx->stab_section_info)           /* If there *is* any info, */
 663     complain (&stab_info_mismatch_complaint, filename);
 664 }
 665 \f
 666 /*  Register that we are able to handle ELF object file formats and DWARF
 667     debugging formats.
 668
 669     Unlike other object file formats, where the debugging information format
 670     is implied by the object file format, the ELF object file format and the
 671     DWARF debugging information format are two distinct, and potentially
 672     separate entities.  I.E. it is perfectly possible to have ELF objects
 673     with debugging formats other than DWARF.  And it is conceivable that the
 674     DWARF debugging format might be used with another object file format,
 675     like COFF, by simply using COFF's custom section feature.
 676
 677     GDB, and to a lesser extent BFD, should support the notion of separate
 678     object file formats and debugging information formats.  For now, we just
 679     use "elf" in the same sense as "a.out" or "coff", to imply both the ELF
 680     object file format and the DWARF debugging format. */
 681
 682 static struct sym_fns elf_sym_fns =
 683 {
 684   "elf",                /* sym_name: name or name prefix of BFD target type */
 685   3,                    /* sym_namelen: number of significant sym_name chars */
 686   elf_new_init,         /* sym_new_init: init anything gbl to entire symtab */
 687   elf_symfile_init,     /* sym_init: read initial info, setup for sym_read() */
 688   elf_symfile_read,     /* sym_read: read a symbol file into symtab */
 689   elf_symfile_finish,   /* sym_finish: finished with file, cleanup */
 690   elf_symfile_offsets,  /* sym_offsets:  Translate ext. to int. relocation */
 691   NULL                  /* next: pointer to next struct sym_fns */
 692 };
 693
 694 void
 695 _initialize_elfread ()
 696 {
 697   add_symtab_fns (&elf_sym_fns);
 698 }